Wellbore annular pressure control system and method using gas lift in drilling fluid return line
First Claim
1. A system comprising:
- a drill string extending into a wellbore below a bottom of a body of water;
a primary pump for selectively pumping a drilling fluid through the drill string and into an annular space created between the drill string and the wellbore;
a riser extending from a top of the wellbore to a platform on a surface of the body of water;
a fluid discharge conduit in fluid communication with the riser;
a controllable orifice choke coupled to the discharge conduit;
a fluid return line extending from the choke to the platform;
a source of compressed gas coupled to the fluid return line at a selected depth below the surface of the body of water;
a separator coupled to the fluid return line;
a flow meter coupled to a gas discharge end of the separator; and
a controller configured to receive an input signal from the flow meter and configured to compare a flow rate of gas measured by the flow meter to a flow rate of gas pumped into the fluid return line.
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Accused Products
Abstract
A system and method include pumping drilling fluid through a drill string extended into a wellbore extending below the bottom of a body of water, out the bottom of the drill string and into the wellbore annulus. Fluid is discharged from the annulus into a riser and a discharge conduit. The riser is disposed above the top of the wellbore and extends to the water surface. The discharge conduit couples to the riser and includes a controllable fluid choke. A fluid return line is coupled to an outlet of the choke and extends to the water surface. Gas under pressure is pumped into the return line at a selected depth below the water surface. The controllable fluid choke may be operated to maintain a selected drilling fluid level in the riser, the selected fluid level being a selected distance below the water surface.
26 Citations
17 Claims
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1. A system comprising:
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a drill string extending into a wellbore below a bottom of a body of water; a primary pump for selectively pumping a drilling fluid through the drill string and into an annular space created between the drill string and the wellbore; a riser extending from a top of the wellbore to a platform on a surface of the body of water; a fluid discharge conduit in fluid communication with the riser; a controllable orifice choke coupled to the discharge conduit; a fluid return line extending from the choke to the platform; a source of compressed gas coupled to the fluid return line at a selected depth below the surface of the body of water; a separator coupled to the fluid return line; a flow meter coupled to a gas discharge end of the separator; and a controller configured to receive an input signal from the flow meter and configured to compare a flow rate of gas measured by the flow meter to a flow rate of gas pumped into the fluid return line. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method comprising:
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pumping drilling fluid through a drill string extended into a wellbore extending below a bottom of a body of water, out the bottom of the drill string, and into the wellbore annulus; discharging fluid from the wellbore annulus and into a riser disposed above the top of the wellbore, the riser extending to the surface of the body of water, discharging fluid from the riser through a fluid return line, the fluid return line extending from below the surface of the body of water to the surface of the body of water; pumping gas under pressure into the return line at a selected depth below the surface of the body of water; maintaining a selected hydrostatic pressure in the riser at a selected distance below the surface of the body of water; separating the gas from a fluid returned by the return line proximate the surface of the body of water; measuring a flow rate of the gas separated from the fluid returned by the return line; and comparing the flow rate of the gas separated from the fluid returned by the return line to a flow rate of the gas pumped into the return line. - View Dependent Claims (11, 12)
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13. A method comprising:
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pumping drilling fluid through a drill string extended into a wellbore extending below the bottom of a body of water, out the bottom of the drill string, and into the wellbore annulus; discharging fluid from the wellbore annulus into a riser disposed above the top of the wellbore and into a discharge conduit, the discharge conduit including a fluid choke and a fluid return line coupled to an outlet of the fluid choke and extending to the water surface; pumping gas under pressure into the return line at a selected depth below the water surface; controlling a rate at which the gas is pumped into the return line and operating a back pressure pump to apply back pressure to the discharge conduit to maintain a level of fluid in the riser at a selected distance below the surface of the body of water; wherein a controller receives input signals from at least one of a pressure sensor in the discharge conduit, a first flow meter coupled to a liquid discharge end of a separator configured to separate the gas from the fluid in the return line, and a second flow meter coupled to a gas discharge end of the separator, and wherein the controller sends output signals to operate the fluid choke and the back pressure pump to maintain the level of fluid in the riser at the selected distance below the surface of the body of water. - View Dependent Claims (14, 15, 16, 17)
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Specification